Former CCM pages

COMMISSION ON CLASSIFICATION OF MINERALS (CCM)

CURRENT INFORMATION

IGC-32 in Florence (20-28th of August, 2003): All the members of CCM are kindly invited to submit
their presentations to the General symposium G 15.03 titled "Crystal
structures of minerals: topology and classification" (convenors:
D.Pushcharovsky, E.Tillmanns). More information may be obtained at the
web site: http://www.32igc.org/home.htm. The deadline for abstract submission is January 28, 2004.

GENERAL INFORMATION

I. Objectives.

The aim of CCM is to collect, document and to help improve existing
or proposed classifications of minerals. The CCM intends to maintain
informed all the members of IMA about the new developments on the
classification of minerals, and to promote meetings for their
discussion.

II. The various classifications of minerals.

It is well known that the classification of minerals has changed
throughout the ages the criterion of classification following the
development of the mineralogical science. The criterion was first based
on practical purposes, then on physical properties, later on chemical
properties. Mineral classification today is largely structural, when the
relation and hierarchy between minerals are based on structure
similarity.

The ancient classification of minerals was mainly based on their
practical uses, minerals being classified as gemstones, pigments, ores,
etc., according to Theophrastos (372-287 B.C.) and to Plinius (77 A.D.).
In the middle ages Geber (Jabir Ibn Hayyaan, 721 - 803) proposed a
classification of minerals based on the external characters and on some
physical properties such as fusibility, maleability and fracture. This
physical classification was developed by Avicenna (Ibn Sina, 980-1037),
Agricola (1494-1555) and A.G.Werner (1749-1817), published by his
student, L. A. Emmerling (1799). This system was substantially refined
by F. Mohs (1773-1839) as Natural-History System of Mineralogy (Dresden,
1820), and used in the first editions of the System of Mineralogy by
J.D. Dana (since 1837). With Werner the physical classification attained
its maturity, and was generally adopted at the end of the XVIII
century. However, it became far too complicated. For instance, Werner
mentioned 54 varieties for colour. A.F.Cronstedt (1722-1765) seems to be
the first to have outlined a classification whereby the chemical
properties were taken first, followed by the physical properties. R. J.
Hauy (1743-1822), in Traité de Minéralogie (1801), presented a mineral
classification based on the nature of metals or, as he would say now,
the nature of cations.

With the development of chemistry the chemical properties became more
and more important, and J.J.Berzelius (1779-1848) in 1819 proposed a
chemical classification of minerals. He recognized that minerals with
the same non-metal (anion or anionic group) had similar chemical
properties and resembled one another far more than minerals with a
common metal. He considered minerals as salts of anions and anionic
complexes: F-, Cl-, Br-, I-, O2-, S2-, Se2-, Te2-, NO3-, CO32-, BO33-,
SO42-, PO43-, SiO44-, BO43-, that is to say, as chlorides, sulphates,
silicates, etc., and not as minerals of zinc, copper, etc. (1814, 1824).
At this time Christian Samuel Weiss (1780-1856) introduced the seven
crystal systems (1815) and Mitscherlich discovered isomorphy (1819) and
polymorphy (1824). J.M.Dana, the founder of Dana System of Mineralogy,
strongly contributed to the development of the chemical approach (1850,
1854, 3-rd and 4-th editions). With this knowledge, Gustav Rose
(1798-1873) combined chemistry, isomorphy and morphology to produce a
chemical-morphological mineral system: I - Elements, II - Sulfides, III -
Halides, and IV - Oxygen compounds, divided into simple and complex
oxides, as carbonates, phosphates, silicates, borates, sulfates. The
highest standard of this classification was achieved in the System of
Mineralogy by E. S. Dana (1892) and in five editions of Tabellarische
Übersicht der Mineralien nach ihrer Kristallographisch-chemischen
Beziehungen (1874, 1882, 1921) by P. v. Groth (1843-1927), that made
this classification widely accepted.

After 1913, when the first structures of minerals were determined,
the structural criterium for classification was taken into account. The
first classifications of this type, which take in consideration the
distribution of bonds in a structure, are that of silicates proposed by
Machatschki (1928), Naray-Szabo (1930) and developed by Bragg (1930).
This chemical-plus-structural classification has been applied to many
other branches of mineralogy such as fluoraluminates (Pabst, 1950),
aluminosilicates (Liebau, 1956), silicates and other minerals with
tetrahedral complexes (Zoltai, 1960), phosphates (Liebau, 1966;
Corbridge, 1971), sulfosalts (Makovicky, 1981, 1993), borates (Strunz,
1997).H. Strunz introduced a chemical-structural classification of the
entire domain of minerals (Mineralogische Tabellen, 1941), followed by
A.S.Povarennykh with a modified classification (1966 in Russian, 1972 in
English). The chemical-structural classification of H.Strunz has gone
through a number of editions, and is currently in the process of being
refined in the light of recent crystal-structure determinations. In the
current system, minerals are divided into 10 major compositional classes
(1)elements, 2)sulfides, 3)halides, 4)oxides, 5)nitrates, carbonates,
6)borates, 7)sulfates, 8)phosphates, 9)silicates, 10)organic compounds)
which are subdivided into divisions, families and groups on the basis of
chemical composition and crystal structure. The paragenetic
classification (Kostov, 1975) is based not only on chemical and
structural pecularities of minerals, but also on the geochemical
similarities of their main cations as well as on their morphology.

The structural classification of minerals was first proposed by
J.Lima-de-Faria in 1983. It corresponds to the application of the
general structural classification of inorganic compounds (Lima-de-Faria
& Figueiredo, 1976) to minerals, which are an integral part of them.
The most general approach to the structural systematics is based on the
analysis of the strength distribution in crystal structures and of the
directional character of the bonds. There are atoms that are more
tightly bounded, and these assemblages are called structural units. They
are considered as the main basis for the structural classification of
minerals. Thus there are five main categories of structures: atomic or
close-packed, group, chain, sheet and framework according to their
dimensionality. This approach to the analysis of the crystal structures
was approved by IUCr Commission on Crystallographic Nomenclature
(Lima-de-Faria et al., 1990). Hawthorn in 1984 and 1985 also proposed a
structural classification of minerals based on the polymerization of
coordination polyhedra. Lima-de-Faria, in 1994, applied the structural
classification to the most common minerals (about 500 minerals organized
in 230 structure types). Detailed structural classification of
silicates was elaborated by F.Liebau (1985).